Ethanol is the principal psychoactive constituent in alcoholic beverages, which are usually consumed with the specific intent of experiencing some of ethanol's effects on the central nervous system. These effects decrease over the course of a few hours, as the ethanol is gradually metabolized by the body into acetyl CoA, a common metabolic product and energy source.
Metabolism of ethanol in the human body is a two-step process (Equation 1), mediated by the enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Unfortunately for the consumer, the immediate metabolite of ethanol, acetaldehyde, is toxic, mutagenic, and carcinogenic.

It can be seen from Equation 1 that when the rate of the ALDH-catalyzed reaction (k2) is not high enough to keep pace with the rate of the ALD-catalyzed dehydrogenation of ethanol (k1), acetaldehyde will accumulate. High acute concentrations of acetaldehyde in vivo (acetaldehydemia) can lead to undesirable effects such as cardiovascular complications, drowsiness, nausea, headache, asthma and facial flushing, while chronic acetaldehydemia can lead to cirrhosis and esophageal cancer. Another unfortunate result of acute acetaldehyde toxicity, well known to heavy drinkers, is the hangover. A person with a hangover will experience dizziness, fatigue, headache, nausea, muscle aches, vomiting, sensitivity to bright light, or sensitivity to noise, and most often a combination of these unpleasant symptoms, for a period of time typically lasting from 12 to 36 hours.
It is well established that acetaldehyde is the culprit in hangovers and in alcohol-induced facial flushing, and it is the principal suspect in alcohol-associated cancers as well vide infra. Acetaldehydemia can occur as a result of heavy alcohol consumption, leading to saturation of ALDH activity, or as a result of light or moderate alcohol consumption in the presence of abnormally high ADH activity or inadequate ALDH activity (k1>>k2 in Equation 1). Inherited defects in both enzyme systems are known to lead to acetaldehydemia-related syndromes. (D. W. Crabb, M. Matsumoto, D. Chang, M. You, Proc. Nutr. Soc. 2004, 63:49-63.)
For example, acetaldehydemia-related facial flushing after light drinking, or upon administration of ethanol-containing pharmaceutical compositions, is experienced by individuals possessing inactive or inefficient aldehyde dehydrogenase (ALDH). (S. Harada, D. P. Agarwal, H. W. Goedde, Lancet. 1981, 2:982.) Inhibition of ALDH by the drug disulfiram creates a similar sensitivity in people having an otherwise normally-acting enzyme. In both cases, there is a reduction of k2 in Equation 1, resulting in a failure to clear acetaldehyde from the blood as rapidly as it is formed, allowing its concentration to reach toxic levels. This type of sensitivity to alcohol-induced flushing is usually associated with the ALDH2*2 allele; possession of which also enhances the risk for esophageal cancer among drinkers. (T. Yokoyama et al., Cancer Epidemiology, Biomarkers & Prevention 2003, 12:1227-1233).
Another means by which ethanol consumption may result in acetaldehydemia is by excessively rapid metabolism of ethanol (i.e., by increasing k1 in Equation 1). Several studies have shown that the presence of ADH2*2 alleles, which encode hyper-active forms of alcohol dehydrogenase (W. F. Bosron, T. K. Li, Hepatology, 1986 6:502-510), also contributes to alcohol flushing and a predisposition to esophageal cancer (A. Shibuya et al., Hum. Genet. 1989, 82:14-16; T. Takeshita et al., Hum. Genet. 1996, 97: 409-413; W. J. Chen et al., Alcohol. Clin. Exp. Res. 1998, 22:1048-1052; A. Yokoyama et al., Alcohol. Clin. Exp. Res. 1999, 23:1705-1710).
From the earliest hangover, people have struggled to find an effective way to treat the disagreeable physical consequences of excessive alcohol consumption. Consumption of additional alcohol is among the oldest of remedies; the expression “Hair of the Dog” has been attributed to the 4th century B. C. Greek playwright Antiphanes. (E. C. Brewer, Dictionary of Phrase and Fable, 1898). While this may temporarily alleviate the symptoms of acetaldehydemia and alcohol withdrawal, it merely postpones the misery and is likely to compound the damage. Other supposedly effective interventions have included a wide variety of foods, vitamins, dietary supplements, exercises and pharmaceuticals. Compounds intended to sequester acetaldehyde in vivo have been designed and evaluated (see, e.g., H. T. Nagasawa et al., J. Med. Chem. 1987, 30:1373-1378), and a wide array of unproven “supplements” and nutraceuticals are marketed to the public as hangover treatments. Notwithstanding the vast trove of folklore and anecdotal evidence, none of these methods has ever been shown to be effective in a clinical trial. (M. H. Pittler et al., BMJ, 2005, 331:1515-1518.)
The alcohol-induced flush reaction (sometimes called “Asian flush” because of its relatively greater occurrence among those of Asian descent) is a set of symptoms experienced by a person having an enzyme abnormality related to the metabolism of ethanol. When an affected person consumes alcohol, there is a rapid build-up of acetaldehyde in his system, due to an aldehyde dehydrogenase deficiency and/or an excess of alcohol dehydrogenase activity. This build-up causes erythema (reddening due to capillary dilation) of the face, neck, and shoulder of the person; the person may also experience nausea, headaches, light-headedness, and an increased pulse rate. The sensations are sufficiently unpleasant that the affected individuals frequently refrain from drinking entirely, and they may be discouraged from the use of ethanol-containing pharmaceuticals. Drugmakers wishing to address this problem have had to surrender ethanol's advantageous physical properties, low cost, and relative safety. As with hangovers, there remains a need for compositions and methods that reliably address the problem of ethanol-induced flushing.
The deuterium isotope effect is a well-known phenomenon in the fields of enzymology and pharmacodynamics. The primary isotope effect can be especially large, and deuterium substitution of enzymatically-removed hydrogens can slow the rate of metabolism of substrates in vivo by a factor of two or three. In particular, it is well-established that appropriate deuteration of a substrate, by slowing the rate of metabolism, can reduce the concentration of metabolites in vivo. An early and pertinent example is the effect of deuteration of the N-methyl group of morphine: metabolism in vivo is slowed by a factor of about two, lowering the blood level of the pharmacologically active metabolite and causing a corresponding reduction in analgesic potency (C. Elison et al., Science, 1961, 1078-1079).
Deuterated drugs have been the subject of a number of patent applications. U.S. Pat. No. 5,223,269 to Liepins describes methods and compositions for treating hypertension. U.S. Pat. No. 5,838,375 to Furminger describes pharmaceutical compositions containing a biological agent and D2O to improve the stability of the agent. U.S. Pat. No. 5,895,660 to Hoffmann describes deuterated drugs for transdermal applications. U.S. Pat. No. 6,376,531 describes deuterated pharmaceuticals for the treatment of psychiatric disorders. The contents of these patents are incorporated by reference into this document in their entirety, for all purposes.
The hydrogen atoms at C-1 in ethanol are enantiotopic; by convention the oxygen and the C-1 and C-2 carbons define a plane which divides the surrounding space, and the hydrogen residing in the “Si” half-space is specified as H(Si) or HSi. The hydrogen in the “Re” half-space is designated as H(Re) or HRe. In the case of ethanol, an alternative terminology designates HRe as the “pro-R” hydrogen, and HSi as “pro-S”. The absolute stereochemistry is shown below:

In the course of oxidation by a mammalian alcohol dehydrogenase, HRe of ethanol is stereospecifically removed and transferred to the enzyme cofactor NAD, with concurrent abstraction of the hydroxyl proton. This produces acetaldehyde as the product, in which HSi has been retained as the aldehydic hydrogen.
Remarkably, despite thousands of years of effort directed to lessening the unpleasant effects of excess ethanol consumption, and more recent attempts to alleviate problems associated with administration of ethanol-containing pharmaceutical formulations, there is still a need for compositions and methods that effectively address these problems.